fix(teams): support single-tenant bots via TEAMS_APP_TENANT_ID env var

[xodn348]

Summary

• BotFrameworkAdapterSettings now receives channel_auth_tenant from the TEAMS_APP_TENANT_ID environment variable, enabling single-tenant Azure Bot registrations.
• When TEAMS_APP_TENANT_ID is unset the value is None, preserving the existing multi-tenant behaviour.
• Two new unit tests cover both code paths (with and without tenant id).

Related issue

Closes #2919 — MS Teams integration supports only deprecated multi tenant bots

Local verification

=== LOCAL_TEST_PASSED ===
$ cd backend && CYPRESS_INSTALL_BINARY=0 uv sync --extra tests
$ uv run pytest tests/test_teams_adapter.py -v
PASSED tests/test_teams_adapter.py::test_teams_adapter_without_tenant
PASSED tests/test_teams_adapter.py::test_teams_adapter_with_tenant
2 passed in 0.35s
$ uv run ruff check chainlit/teams/app.py tests/test_teams_adapter.py
All checks passed!
$ uv run ruff format --check chainlit/teams/app.py tests/test_teams_adapter.py
All checks passed!

Risk

Low. One-line change; the new parameter is optional and defaults to None (same as the previous implicit default). No behaviour change for existing multi-tenant deployments.

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Summary by cubic

Enable single-tenant Microsoft Teams bots by wiring TEAMS_APP_TENANT_ID to BotFrameworkAdapterSettings.channel_auth_tenant (closes #2919). When unset, behavior stays multi-tenant; tests cover both paths.

^{Written for commit 1c86d64. Summary will update on new commits. Review in cubic}

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}